Which of the following cables is made of glass or plastic and transmits signals in the form of light?

A.
Coaxial cable

B.
Twisted pair cable

C.
Plenum cable

D.
Fiber optic cable

Explanation:

Fiber optic cable is also known as optical fiber. It is made of glass or plastic and transmits signals
in the form of light. It is of cylindrical shape and consists of three concentric sections: the core, the
cladding, and the jacket. Optical fiber carries much more information than conventional copper
wire and is in general not subject to electromagnetic interference and the need to retransmit
signals. Most telephone company’s long-distance lines are now made of optical fiber.
Transmission over an optical fiber cable requires repeaters at distance intervals. The glass fiber
requires more protection within an outer cable than copper.
Answer option B is incorrect. Twisted pair cabling is a type of wiring in which two conductors (the
forward and return conductors of a single circuit) are twisted together for the purposes of canceling
out electromagnetic interference (EMI) from external sources. It consists of the following twisted
pair cables:
Shielded Twisted Pair: Shielded Twisted Pair (STP) is a special kind of copper telephone wiring
used in some business installations. An outer covering or shield is added to the ordinary twisted
pair telephone wires; the shield functions as a ground. Twisted pair is the ordinary copper wire that
connects home and many business computers to the telephone company. Shielded twisted pair is
often used in business installations. Unshielded Twisted Pair: Unshielded Twisted Pair (UTP) is
the ordinary wire used in home. UTP cable is also the most common cable used in computer
networking. Ethernet, the most common data networking standard, utilizes UTP cables. Twisted
pair cabling is often used in data networks for short and medium length connections because of its
relatively lower costs compared to optical fiber and coaxial cable.UTP is also finding increasing
use in video applications, primarily in security cameras. Many middle to high-end cameras include
a UTP output with setscrew terminals. This is made possible by the fact that UTP cable bandwidth
has improved to match the baseband of television signals.
Answer option A is incorrect. Coaxial cable is the kind of copper cable used by cable TV
companies between the community antenna and user homes and businesses. Coaxial cable is

sometimes used by telephone companies from their central office to the telephone poles near
users. It is also widely installed for use in business and corporation Ethernet and other types of
local area network. Coaxial cable is called “coaxial” because it includes one physical channel that
carries the signal surrounded (after a layer of insulation) by another concentric physical channel,
both running along the same axis. The outer channel serves as a ground. Many of these cables or
pairs of coaxial tubes can be placed in a single outer sheathing and, with repeaters, can carry
information for a great distance. It is shown in the figure below:

Answer option C is incorrect. Plenum cable is cable that is laid in the plenum spaces of buildings.
The plenum is the space that can facilitate air circulation for heating and air conditioning systems,
by providing pathways for either heated/conditioned or return airflows. Space between the
structural ceiling and the dropped ceiling or under a raised floor is typically considered plenum.
However, some drop ceiling designs create a tight seal that does not allow for airflow and
therefore may not be considered a plenum air-handling space. The plenum space is typically used
to house the communication cables for the building’s computer and telephone network.